WO2018146444A1

WO2018146444A1 - Separation of liquid droplets from gas

Info

Publication number: WO2018146444A1
Application number: PCT/GB2018/050095
Authority: WO
Inventors: Javier VIÑUALES NAVARRO; Robin PITT
Original assignee: Hieta Technologies Limited
Priority date: 2017-02-13
Filing date: 2018-01-15
Publication date: 2018-08-16
Also published as: GB2559610B; GB2559610A; GB201702324D0

Abstract

A separator (2) for separating liquid droplets from a gas comprises an inertial separator array (4) comprising a repeating pattern of elements (6), each element of the repeating pattern comprising a separate inertial separation structure to perform inertial separation of the liquid droplets from a respective portion of the gas. The separator array (4) can be combined with a heat exchanger (20) so that each group of one or more heat exchanger channels (22) has its own separate inertial separation structure 6 for separating liquid droplets from the gas passed by the heat exchanger channel (22).

Description

SEPARATION OF LIQUID DROPLETS FROM GAS

The present technique relates to the field of engineering. More particularly, it relates to a separator for separating liquid droplets from a gas.

Some engineering systems may output a gas containing liquid droplets or vapour. For example, the exhaust gas from an internal combustion engine may include water vapour. Recovery of the water from the exhaust gas can allow the heat energy held by the water to be harnessed, or allow the recovered water to be used as coolant in another part of the engine. Hence, the exhaust path may include a condenser for condensing the vapour into liquid and the liquid droplets can then be separated from the gas by a separator. Another example may be in a proton exchange membrane fuel cell, which may generate water as a by-product of the reaction between hydrogen and oxygen used to generate an electrical current, as well as requiring water as an input for wetting the membrane. A condenser may be provided for condensing steam output from the fuel cell and separating the condensed water droplets from other gases output by the fuel cell. However, typical separators for separating liquid from a gas can be relatively large, which can be a problem for some engineering applications, such as in automotive fields where the space available for an engine or fuel cell under the bonnet may be limited.

At least some examples provide a separator for separating liquid droplets from a gas, comprising:

an inertial separator array comprising a repeating pattern of elements, each element of the repeating pattern comprising a separate inertial separation structure to perform inertial separation of the liquid droplets from a respective portion of the gas.

At least some examples provide a method of manufacturing a separator for separating liquid droplets from a gas, comprising:

forming an inertial separator array comprising a repeating pattern of elements, each element of the repeating pattern comprising a separate inertial separation structure to perform inertial separation of the liquid droplets from a respective portion of the gas.

At least some examples provide a computer-readable data structure representing a design of a separator as described above.

Further aspects, features and advantages of the present technique will be apparent from the following description of examples, which is to be read in conjunction with the accompanying drawings, in which:

Figure 1 schematically illustrates an example of a separator comprising an inertial separator array of repeating elements each providing an inertial separation structure for separating liquid droplets from gas by inertial separation;

Figure 2 illustrates an example of providing the separator at the outlet of a heat exchanger;

Figure 3 illustrates an example of providing the separator at the inlet of a heat exchanger; Figures 4 to 7 illustrate different views of a portion of a heat exchanger and separator for separating liquid droplets from the gas output by the heat exchanger;

Figure 8 illustrates computational fluid dynamics (CFD) simulation results illustrating a gas path through one of the inertial separation structures of the embodiment of Figures 4 to 7;

Figure 9 illustrates a condenser unit comprising pre- and post-separation stages for separating liquid droplets from gas at the inlets and outlets of a heat exchanger;

Figures 10 to 15 illustrate different views of a weir unit used at the pre-separation stage;

Figures 16 to 19 illustrate different views of a swirl tube unit used at the post-separation stage; and

Figure 20 illustrates a method of manufacturing a separator using additive manufacturing.

In a gas containing liquid droplets to be separated from the gas, the liquid droplets are typically larger than the gas particles and so have higher inertia. Inertial separation techniques exploit this to separate the liquid from the gas. For example, the gas containing the liquid droplets can be guided through a path with a geometry which makes the lighter gas particles more likely to follow a path to a gas outlet than the liquid. However, typically, when liquid needs to be filtered from a given volume of gas, a single large separator is provided for separating the liquid droplets from the entire volume. In contrast, the inventors recognised that splitting the overall volume of gas into a number of smaller portions, and performing inertial separation of liquid droplets from the respective portions of the gas separately for each portion using a number of independent inertial separation structures, allows the overall size of the separator to be reduced, for a number of reasons. Firstly, inertial separation can be performed more effectively at a smaller scale because pressure losses are lower due to lower Reynolds numbers for a narrower channel. Also, if each inertial separation provides a bend, incline or other deviation in the gas flow path, typically the overall volume of the array as a whole can be smaller than if a single large bend, incline or deviation is provided, allowing the overall packing efficiency to be improved (even when accounting for the increased number of separation structures), which can be important for automotive applications or other applications where space is limited and so packing efficiency is an important factor. Providing separate inertial separation structures also can allow better integration with other elements for conveying the gas, such as a heat exchanger.

In one example, each inertial separation structure comprises at least one gas inlet for receiving the gas containing the liquid droplets, at least one gas outlet for outputting the separated gas, and a collector for collecting the separated liquid droplets. A fluid flow path from a gas inlet to a gas outlet may bend more sharply than a fluid flow path from the gas inlet to the collector. Hence, the larger size liquid droplets may be less likely to travel round the bend than the gas, separating the liquid from the gas.

The separator may also comprise a heat exchanger comprising an array of heat exchanging channels for conveying the gas. The heat exchanger may comprise an array of coolant channels for conveying coolant for cooling the gas in the heat exchanging channels. For example, if the liquid in the gas entering the separator is still in a vapour phase, the heat exchanger can be used to cool the gas and condense the vapour to form liquid droplets, which can be separated by the inertial separation structures.

It can be particularly useful to combine the inertial separator array with a heat exchanger, as each inertial separation structure can be arranged to correspond to a given group of one or more heat exchanging channels, so that each group of heat exchanging channels has its own local inertial separation structure. This has several advantages. Firstly, providing smaller local separation at each group of heat exchanging channels helps improve packing efficiency since this reduces the need for ducting to collect the gas from each of the heat exchanging channels and combining the gas into a single wide channel to pass to a single combined separator.

Also, where the heat exchanger is used to cool the gas to condense the liquid, in practice the liquid will form as a film at the walls of the heat exchanger channels (closest to the adjoining coolant channels). It is typically more efficient to separate films of liquid which are already gathered together from the remaining gas than to separate discrete liquid droplets which are mixed through the gas. If the gas from the respective heat exchanger channels is combined into a single wide tube and provided to a single separator, firstly it is more likely that the films of liquid running down the walls of the heat exchanger channels will disperse and be mixed through the gas, and secondly the hotter gas in the middle of the heat exchanger channels will have more time to heat the liquid so that some liquid may return to the gas phase. Both these factors mean that a single combined separator shared between the heat exchanger channels as a whole will typically be less efficient at separating the liquid from the gas. In contrast, where separate smaller structures are provided for local inertial separation of each group of heat exchanger channels, the film of liquid at the walls of the heat exchanger channels is easier to extract as it stays intact and is less likely to be boiled off by hotter gas before it reaches the inertial separator structures.

For all these reasons, providing a heat exchanger with a number of heat exchanging channels for conveying gas, together with an array of inertial separation structures at the outlets of each group of one or more heat exchanger channels, with each inertial separation structure performing inertial separation of liquid from the gas conveyed by the corresponding group of heat exchanging channels, allows more efficient separation of liquid from the gas. Computational fluid dynamics (CFD) simulation results demonstrating the improved performance of the distributed separation approach compared to a single large separator are discussed below.

In some cases, the heat exchanger may precede the inertial separator array. Hence, each inertial separation structure may be configured to perform the inertial separation after the gas is passed through the corresponding group of heat exchanging channels of the heat exchanger. This can be useful to allow the heat exchanger to act as a condenser for forming the liquid which is to be separated by the inertial separator array. However, in other examples, the heat exchanger may follow the inertial separator array, so that each inertial separation structure is configured to perform the inertial separation prior to the gas being passed through the corresponding group of one or more heat exchanging channels. The heat exchanger could be provided for cooling or heating the gas, and may function more efficiently if the gas contains less liquid dispersed through the gas. Hence, by providing inertial separation structures at the inlets of the respective groups of heat exchanger channels, more efficient separation of the liquid from the gas can be achieved to improve heat exchanger performance.

In some cases, inertial separation could be performed both at the inlets and the outlets of the heat exchanger. Hence, the separator may comprise a first inertial separator array arranged to perform the inertial separation prior to the gas being passed through the heat exchanger, and a second inertial separator array arranged to perform the inertial separation after the gas is passed through the heat exchanger. The first and second inertial separator arrays could have the same configuration, or could have different designs. Providing inertial separator arrays at both the inlets and outlets of the heat exchanger can be particularly useful where the heat exchanger functions as a condenser for condensing liquid droplets from the gas, as the first inertial separator array can remove pre-existing liquid from the gas, allowing the heat exchanger to be more efficient at condensing liquid from the gas, before the second inertial separator array then collects the liquid condensed by the heat exchanger. In other words, an apparatus may be provided comprising a heat exchanger comprising a plurality of heat exchanging channels for cooling a gas, a pre-separation stage to separate liquid droplets from the gas prior to the gas being passed through the heat exchanger, and a post-separation stage to separate liquid droplets from the gas after the gas is passed through the heat exchanger.

In some examples, the inertial separator array may be integrally formed with the heat exchanger. For example, the inertial separator array and heat exchanger may be formed in a single process, e.g. by additive manufacturing. The added complexity of forming the inertial separation structures at the inlets or outlets of the heat exchanger channels may involve less manufacturing cost than manufacturing an entirely separate inertial separator, so it can be more efficient to form the inertial separator array as an integral part of the heat exchanger.

On the other hand, other examples may form the inertial separator array and the heat exchanger from separately formed modules. The technique can be useful even if the pitch of the inertial separator structures is not aligned precisely with the pitch of the heat exchanger structures - e.g. the gas from the heat exchanger channels may simply guided into whatever inertial separator structure is nearest, rather than being manufactured with a precise one-to-one or many-to-one relationship between the heat exchanger channels and the inertial separation structures. Hence, in some cases the inertial separator array could be manufactured separately and used with an existing heat exchanger module.

The inertial separation structures may take different forms. In one example, the inertial separator array comprises two or more rows, with each row comprising a collection trough running along the row, and at least one gas outlet window arranged between at least one gas inlet for receiving the gas containing the liquid droplets and a base of the collection trough. In some examples, the at least one gas outlet window may be arranged in a side of the collection trough a distance away from the base of the collection trough. Hence, when the gas enters the inlet, the lighter gas particles are more likely to divert through the window than the liquid droplets, which gather in the collection trough. Also, gas which hits the base of the trough is more likely to flow back up the sides of the trough to the gas outlet window than the liquid. The gas outlet window could be a continuous slot running along the length of the trough, or a number of discrete windows at various points along the length of the trough.

Where the inertial separator array is combined with a heat exchanger, one row of the inertial separator array can correspond to a single heat exchanger channel or to multiple heat exchanger channels. For example, the heat exchanger may comprise several rows of heat exchanger channels, each row containing one or more heat exchanging columns, and each row of channels may correspond to one row of the inertial separator array.

Each inertial separation structure may comprise a shielding portion to shield the at least one gas outlet window from an incoming flow of gas containing liquid droplets. For example, the shielding portion may comprise a rim portion protruding around at least part of each gas outlet window. For example, the shielding portion could be a ledge extending over the window at least on the side facing the direction of incoming gas. Hence, when in use, the gas containing the fluid may hit the rim portion and be diverted away from the window, with the higher inertia of the liquid droplets making it less likely that the liquid goes back through the window.

The rim portion may in some examples include surfaces which meet at a point pointing towards the gas inlets. This will tend to split the flow of gas hitting the rim of the outlet window to guide the gas to either side of the window, making it less likely that the gas flows over the rim and directly through the window itself (which would increase the likelihood of liquid droplets passing through the window). Hence, by guiding the gas to either side of the window, the liquid is more likely to be collected in the collection trough. Making the rim portion meet at a point at the top of the window also has the advantage of enabling the inertial separation structures to be made by additive manufacturing, as it would be difficult to make a flat overhanging rim above the window through additive manufacturing techniques. Although the rim portion could be formed only on the side of the gas outlet window facing the gas inlets, in some examples the rim portion could be formed along the sides of the window parallel to the gas flow direction as well. This can be useful, as it means that the rim portion can have a constant thickness all the way up the window, so that there is no overhanging portion which be difficult to manufacture using additive manufacturing. In some examples a fin for partitioning a row of heat exchanger channels into multiple channels can be formed to extend from the apex of the rim portion of the gas outlet window. Again, this assists with making the design suitable for additive manufacturing, as the rim portion provides a support for allowing the layers of the fin to be built up on top of the rim. In another example, the gas flow direction could be across the rows of inertial separation structures, rather than in a column direction towards the base of the collection troughs. This approach can be particularly useful where the inertial separator array acts as a pre-separation stage for a subsequent heat exchanger, as the inertial separator array can also act to divide a larger gas flow into smaller portions to be guided down each separate heat exchanger channel. With this approach, the rows of collector troughs may effectively form a corrugated surface of peaks and troughs, with the gas from the inlet passing over the respective peaks and troughs to be distributed among the various structures. In this case, for each inertial separation structure, the at least one gas outlet window can be disposed on the side of the collector trough that faces away from the at least one gas inlet, so that it is shielded from the incoming flow of gas by the other side of the same peak. That is, the shielding portion for the window in one inertial separation structure may effectively be the side of the collector trough in a neighbouring row that faces towards the at least one gas inlet. Hence, with this approach there may be no need to form a protruding rim around the gas outlet windows as the peaks between adjacent collector troughs may already shield the gas outlet windows from the incoming flow of gas, making it harder for the heavier liquid droplets to enter the windows than the lighter gas particles.

The inertial separation structures may in general be arranged in a periodic pattern of repeating elements, such as a row pattern as discussed above, or a grid pattern. The grid pattern could be a square, rectangular or hexagonal grid pattern for example. Where the separation structures are substantially circular or elliptical, a hexagonal packed pattern can be particularly useful to achieve a higher packing density.

In another example, the inertial separation structures may use centrifugal or cyclonic motion to separate the liquid from the gas. For example, each inertial separation structure may comprise a tubular housing and swirl inducing vanes to induce a swirling flow of gas and liquid droplets within the tubular housing. The tubular housing could have an elliptical or polygonal cross-section, but a circular cross-section can be most efficient in terms of performance. The vanes may be arranged to direct the flow of gas and liquid droplets towards an inner wall of the tubular housing, and the higher inertia of the liquid droplets may make it less likely that the liquid droplets make it back towards the axis of the tubular housing. Hence, by providing at least one collecting portion at an inner wall of the tubular housing for collecting the liquid droplets, and at least one gas outlet closer to an axis of the tubular housing than the at least one collecting portion, most of the liquid droplets can be separated from the gas, as the liquid will typically run down the inner wall of the tubular housing while the gas may swirl back towards the axis.

The separator may comprise liquid ducting to direct the liquid separated by each of the plurality of inertial separation structures to a combined liquid outlet. For example, the network of liquid ducting could have a rectangular grid arrangement or hexagonal grid arrangement, gathering the liquid collected by each structure and directing it to a common outlet point, where the liquid can be tapped for use elsewhere in the system. Hence, rather than providing gas ducting for combining the gas before separation, the liquid is combined after separation, allowing for more efficient separation of the liquid from the gas for the reasons given above. The remaining gas after separation could also be combined into a common flow or could remain in individual channels.

In some cases, the separator may be formed from at least one separator module, each separator module comprising an integrally formed array of two or more inertial separation structures arranged in the repeating pattern. By forming the separator from a modular structure where a number of modules of some unit size (including at least two of the inertial separator structures) can be combined as desired to form larger structures, this allows the technique to be easily scaled to larger or smaller heat exchangers for example. A single one of the modules may be manufactured in an integrated process, e.g. through additive manufacturing, but then more than one module may be combined post-manufacture to form the overall separator array for a given application.

Although the inertial separator array could be formed using techniques such as casting or moulding, it can be particularly useful to form the inertial separator array (and/or the heat exchanger) by additive manufacturing, in which a three-dimensional object is formed by building layer upon layer of material under computer control. For example, selective laser melting could be used. Additive manufacture allows fine control of small structures, such as the windows in some embodiments of the inertial separation structures, which can be difficult to manufacture by other methods.

A computer-readable data structure may be provided, representing a design of a separator described above. The data structure may be stored on a storage medium. The storage medium may be a non-transitory medium. Additive manufacturing techniques may be computer-controlled, where the manufacturing device is automatically controlled based on a design file representing the design of the object to be made. For example, the design file may control the pattern of laser scanning used to scan across a bed of powder which may control the laser to selectively melt portions of the powder to fuse portions together and create layer after layer of the 3D object. Hence, in some cases rather than providing an actual manufactured product, the designer may provide a computer-readable data structure representing the separator to another party, to allow that party to make the product by additive manufacturing themselves. Hence, in some embodiments the technique may be embodied in a computer automated design (CAD) file rather than a physical product.

Specific examples are set out below. It will be appreciated that the invention is not limited to these particular examples.

Figure 1 schematically illustrates an example of a separator 2 for separating liquid droplets from a gas. The separator 2 includes an inertial separation array 4 which includes a repeating pattern of elements, each element comprising a separate inertial separation structure 6 to perform inertial separation of liquid droplets from a respective portion of the gas passed through the separator 2. The inertial separation elements 6 could be arranged side by side in a row, or over a two-dimensional plane, and can be arranged in different patterns (e.g. in linear rows, over two dimensions in a rectangular or square grid pattern, or in a hexagonal packed pattern, for example). Each inertial separation element 6 has a separate gas outlet path 8 and liquid outlet path 10. The geometry of the inertial separation element 6 between a gas inlet and the gas outlet path has a shape for which the probability that particles enter the gas outlet path 8 rather than the liquid outlet path 10 decreases with increasing mass of the particles. Hence, the heavier liquid droplets are more likely to be output in the liquid outlet path 10 than the gas outlet path 8. For example, each inertial separation element 6 may have a fluid flow path between a gas inlet and the gas outlet path 8 which travels around a bend or other discontinuity, so that the heavier liquid particles which have greater inertia find it more difficult to make the turn into the gas outlet path 8. Several examples of different inertial separation structures are discussed below.

Figures 2 and 3 show two examples where the inertial separator array 4 is combined with a heat exchanger 20 including a number of heat exchanging channels 22 for conveying the gas. For example, the heat exchanger 20 may include a series of interleaved hot channels 22 and cold channels 24 with coolant being passed through the cooling channels 24 and hot gas containing liquid or vapour being passed through the hot channels 22. Hence, vapour in the gas is condensed as it passes through the heat exchanger due to the cooling provided by the cooling channels 24.

In Figure 2, the separator 2 comprises the inertial separator array 4 at the outlet of the heat exchanger 20, for separating liquid from the gas passed out of the heat exchanger 20. Each inertial separation structure 6 corresponds to a group of one or more heat exchanger channels 22 of the heat exchanger 20 and separates liquid from the gas passed through the corresponding group of heat exchanger channels 22. Hence, condensate collected by cooling the vapour within the heat exchanger can be removed by the separator 4 with the respective inertial separation elements 6 each acting on a respective portion of the gas passed by the heat exchanger.

On the other hand, in Figure 3 the separator 2 comprises the inertial separator array 4 at the inlet of the heat exchanger 20, for separating liquid from the gas before it is passed into the heat exchanger 20. It may seem counterintuitive to provide separation of liquid before the gas enters the heat exchanger for cooling. However, in practice even if the heat exchanger is to be used for condensing vapour into liquid, the gas entering the heat exchanger may already contain some liquid droplets (which could be the same liquid as the condensate to be condensate or other liquids - e.g. the exhaust gas of a combustion engine may include some droplets of fuel as well as the water vapour to be condensed). The presence of liquid droplets in the gas may reduce the heat exchanger performance making it more difficult to extract as much condensed liquid from the gas. By providing a pre-separation stage for the heat exchanger, any pre-existing liquid can be separated out, before condensing the vapour contained in the gas into further liquid using the heat exchanger, to provide improved heat exchange efficiency. While not shown in Figure 3, a further separator array 4 can be provided at the outlet of the heat exchanger 20 in the same way as in Figure 2, to allow the condensed liquid to be separated from the gas. It will be appreciated that while Figures 1 to 3 show different paths for the separated gas and separated liquid, in practice the separator 4 may not be able to separate out 100% of the liquid droplets contained in the gas and so some liquid droplets may still pass through the gas outlets 8. While it is possible for some implementations to be designed to give 100% effectiveness for separating droplets of a certain minimum droplet size, with a more aggressive design this may come at the penalty of higher pressure drop, and so some implementations may choose to provide a separation fraction of less than 100% for a given droplet size in order to trade off separation against other performance factors. Nevertheless, the majority of the liquid droplets can be separated out.

The combined heat exchanger / separator in Figures 2 or 3 can be formed as an integrated unit. For example, the heat exchanger 20 and separator array 4 can be formed as a single block of material (e.g. through an additive manufacturing process), which cannot be separated from one another after manufacture. Alternatively, the heat exchanger 20 and separator array 4 could be formed as separate modules which are combined after manufacture and can be assembled and disassembled as required. While Figures 1 to 3 shows the heat exchanger in a vertical orientation where the gas travels along the channels from top to bottom, this is not essential and the heat exchanger could also be used in a different orientation.

The cross-section of the hot channels 22 of the heat exchanger can be non-uniform along the width of the channels. In some examples, the channels 22 may have a maximum diameter of less than 10 mm. More particularly, the maximum diameter of the heat exchanger channels 22 may be less than 5 mm, or less than 2 mm, or less than 1 mm, or less than 0.5mm. At such small scales, it would typically be considered impractical to form separate inertial separation structures for each channel or row of channels using standard manufacturing techniques such as moulding or casting, but the inventors of the present technique recognised that hydraulic diameters at such scales are possible using additive manufacturing, to achieve the benefits discussed above.

Figure 4 shows a more detailed example of a separator 2 comprising a heat exchanger 20 and inertial separator array 4. In this example the heat exchanger 20 and separator array 4 are shown as an integrated structure, although in other examples the structure could also be formed out of separate modules. In the example of Figure 4, the heat exchanger channels 22 are formed in rows 40 each bounded by a pair of plates 42 with a number of fins 44 going along the row 40 separating the respective heat exchanger channels 22 into columns within the same row 40. The cold channels 24 are formed between the plates 42 of neighbouring rows. Figure 4 shows one row 40 of the heat exchanger channels 22 and the corresponding inertial separation structure of the separator array 4, as well as a portion of the two neighbouring rows to illustrate the repeating pattern. However, it will be appreciated that the separator 2 in practice may comprise many such rows which may continue repeating in the same pattern shown in Figure 4. Similarly, the heat exchanger 20 may also have a greater number of heat exchanger channels 22 per row. Figures 5, 6 and 7 show views of the separator 2 of Figure 4 when viewed along the three orthogonal directions Y, X and Z respectively as indicated in Figure 4. As shown in Figures 4 to 7, each row 40 of heat exchanger channels has a corresponding inertial separation structure 6 for separating liquid droplets from the gas. Each inertial separation structure includes a collection trough 50 which passes under the corresponding row of heat exchanging channels 22 for gathering the liquid extracted from that group of heat exchanger channels 22. The collection trough 50 has a substantially U- or V-shaped profile with side surfaces 52 tapering towards the bottom of the collection trough 50.

A number of gas outlet windows 54 are formed in the sides of the collection trough 50 running along the row direction 40, for outputting the gas from which the liquid has been extracted. The windows 54 are formed a distance above the base of the trough 50. In other examples the windows could be replaced with a longer slot running along the length of the trough. As shown in Figures 4 and 7, each window 54 is surrounded by a rim portion 56 which protrudes from the side of the collection trough 50. The rim portion 56 acts as a shield for shielding the gas outlet windows 54 from the incoming flow of gas and liquid which flows down the heat exchanging channels 22. The rim portion 56 extends all the way up the sides of the windows and across the top of the window. At the top of the gas outlet windows 54, the rim portion tapers to a point and the apex of the rim portion of each window 54 is connected to one of the fins 44 which divide the respective heat exchanging channels 22 within the same row 40. This is useful because this allows the fins 44 and window rim portions 56 to be made by additive manufacture, since the rim portion 56 can support the fins 44 so that there is no need for an overhanging portion. Each part of the fin 44 and rim 56 surrounding the window is supported by material below it and so can be built up layer by layer using additive manufacture.

As shown in Figure 5, as the gas passes down the heat exchanger channels 22, liquid is condensed out of the gas due to the cooling provided by the cooling channels 24 and so a film 60 of condensed liquid accumulates near the walls of the channels 22. The film runs down towards the inertial separation element 6, and when it reaches the gas outlet windows 54 the tapered rim portion 56 surrounding each gas outlet window directs the film of condensed liquid around the edges of the window (see Figure 7). As the windows have a tapered upper surface of the rim 56, this reduces the chance that liquid can spill over into the window. Hence the liquid is guided to the collection trough 50, where it accumulates in the base of the trough. The liquid runs along the collection trough 50 in the row direction to the ends of the separator 2. Liquid ducting can be provided to gather the liquid from each row and combine the liquid into a single liquid supply outlet.

Hence, as the liquid droplets have a relatively large mass in comparison to the gas, it is relatively unlikely that they will be able to make their way up the collection trough 50 back to the windows. On the other hand, the gas passing through the heat exchanger channels 22 is lighter and can more easily travel around sharp bends. Hence, the gas is able to flow through the gas outlet windows and into the space 62 below the cooling channels 24 of the heat exchanger from where the gas can be output to outside, e.g. as exhaust gas. Hence, this is an example of an inertial separation structure which uses a geometry which forces the gas towards a region where to traverse to the gas outlet space 62, the gas has to travel round a bend which is sharper than any bend required to reach the collector trough 50, and so this makes it more likely that the gas will reach the gas outlet spaces 62 rather than the liquid due to its lower inertia.

Figure 8 shows results of a computational fluid dynamics (CFD) simulation of the gas flow through one of the inertial separation structures. The passage of liquid droplets through the inertial separation structure was also simulated. A similar CFD analysis was performed for a large U bend structure which is used in conventional separators and simply passes the large volume of gas down a vertically oriented tube, round a bend and back up another vertically oriented tube (i.e. around a vertically oriented U shape), with the liquid being tapped off near the base of the U bend. For the U bend structure, it was found that around 60% of water droplets of 10 microns size were recovered. In contrast, for the separator design shown in Figures 4 to 7, around 94% of 10 micron droplets and 100% of 50 micron droplets were collected (any droplets larger than 50 microns were fully collected). Hence, this validates the effectiveness of the separator compared to current designs.

Figure 9 shows an example of a condenser unit 100 which includes two separators both including an array of inertial separation elements. The condenser unit 100 could be used for a range of engineering applications, e.g. for recovering water condensed from steam output by a hydrogen fuel cell, for refrigeration systems, or any other application where water or another fluid needs to be condensed and separated from a gas. As shown in Figure 9, the condenser unit 100 includes an inlet duct 102 where the gas containing liquid droplets and/or vapour is input into the condenser unit 100, a weir unit 104 which provides a pre-separation stage for separating any liquid droplets existing in the gas before condensation from the remaining gas and vapour, a condensing heat exchanger 106 for passing the gas and vapour through a number of heat exchanging channels which are interleaved with coolant channels in order to condense out the vapour contained in the gas, a swirl tube block 108 which provides a post- separation stage for separating the condensed liquid from the remaining gas, and an outlet duct 1 10 for gathering the remaining gas from the respective outlets of the swirl tube block 108 and outputting the gas. The respective components of the condenser unit 100 can be manufactured separately as distinct modules, for example the weir unit 104, heat exchanger 106 and swirl tube unit 108 may each be made separately as a distinct module using additive manufacturing. There is no need for there to be a specific matching between the outlets and inlets of the respective stages, although matching between the outlets/inlets of the respective stages could be implemented. Each of the weir unit 104 and the swirl tube unit 108 includes an array of repeating elements where each repeating element has a separate inertial separation structure for separating liquid droplets from a gas using inertial separation.

Figures 10 to 15 show the weir unit 104 in more detail. As shown in Figure 10, the weir block 104 is formed in a modular fashion from a number of repeating sections 120. In this example the weir block 104 includes five repeating sections 120, with each repeating section including a repeating pattern of inertial separation structures 122 running along that section 120. In this example each repeating section 120 includes 30 weir sections 122, but again a different embodiment may scale the number of weir sections depending on the required geometry of the weir block. By forming the weir block 104 using a modular design in this way it is simple to scale the weir block to different sizes required for a given application. In this example, the different repeating sections 120 are formed in an integrated manner by a single additive manufacturing process. However, it would also be possible to form the repeated sections 120 separately and then lay them side by side to cover a larger area.

Figure 1 1 shows a portion of one of the repeating sections 120 of the weir block 104 in more detail. As shown in Figure 1 1 , the repeating section 120 includes a repeating pattern of inertial separation structures 122 which are arranged in rows across the repeating section 120. Figure 12 shows a cross section through the inertial separation structures 122 of one repeating section 120. As shown in Figures 1 1 and 12 each inertial separation structure includes a collection trough 124 for collecting liquid droplets. Each collection trough 124 is formed between a pair of adjacent ridges 126 which are repeated so that the overall profile of the weir section forms a jagged or sawtooth-like pattern. As shown in Figure 1 1 , each ridge 126 has a number of gas outlet windows 128 formed in one side of the collection trough 124. The surface of the ridge 126 containing the windows is substantially vertical, while the other surface of each ridge slopes down more gently. Figure 1 1 shows many small windows being arranged along the length of each ridge on one side of the trough, but it will be appreciated that each of the small windows could also in some embodiments be replaced with longer slots, or even a single slot which passes along the full length of the row. However, by forming the gas outlet as discreet small windows, this provides better mechanical support, making the unit more robust, as well as making it easier to manufacture the weir unit using additive manufacturing since the pillars between adjacent windows provide support for manufacturing the ridges above the windows to avoid as great an overhang. As shown in Figure 12, the orientation of the weir unit with respect to the inlet duct 102 is such that the gas entering the condenser unit 100 flows across the weir unit in the direction indicated in Figure 12 so that the gas outlet windows 128 are on the side of each ridge 126 that faces away from the gas inlet. This means that the gas outlet windows 128 are shielded from the incoming flow of gas and liquid droplets by the other side of each ridge which faces the gas inlet region.

Figure 13 shows a zoomed in portion of Figure 12 showing the inertial separation structures in more detail and the paths taken by gas and liquid through a given separation structure. Figure 14 shows a zoomed in cross section in a perspective view. As shown in Figure 13, when the gas is input from the right hand side of the structure then the gas spreads out throughout the weir unit and different portions of the gas flow into different rows of inertial separation structures. For a given inertial separation structure, the liquid droplets within the gas have higher inertia due to their increased mass compared to the gas particles, and so it is more difficult for these liquid particles to make the turn into the gas outlet window 128 compared to the gas particles. Hence the liquid droplets tend to hit the tapered front surface 130 of the ridge and fall into the base of the collector trough 124 while the gas particles are able to go through the gas outlet window 128 in the back surface of each ridge 126 and then go round the bend into the gas outlet region. A deflector portion 132 may be formed underneath each ridge to guide the gas into the gas outlet of the weir unit. From here the gas can then be passed into corresponding heat exchanger channels of the heat exchanger unit 106.

The liquid which has settled in the base of the collection trough 124 runs to the end of each repeated section 120 of the weir. As shown in Figure 15, each repeating section of the weir 104 has alternating sections 136 of the ridge 126 which rise and fall in a chevron shape so that the channels 138 at the base of each collector guide the liquid down to the ends of each repeating weir section 120. Larger channels running along the repeating section can then guide the liquid to the ends of the repeating section from where they can be outlet via an outlet hose 140 as shown in Figure 10.

In summary, the weir section provides for pre-filtering of any liquid droplets from the gas before they pass into the condensing heat exchanger. This enables the performance of the heat exchanger to be improved since the cooling provided by the heat exchanger can be used mainly for condensing vapour into liquid rather than cooling existing liquid. By forming the weir section from a repeating pattern of inertial separation structures this provides more efficient separation than a single large U-bend or other structure for filtering liquid from the gas when the gas is still in one mass. Also, the weir unit has a compact form which would be difficult to achieve with separation of a larger volume of gas in one structure. The intricate pattern of inertial separation structures in the weir unit 104 can be manufactured using additive manufacturing techniques.

Figure 16 shows the swirl tube unit 108 in more detail. Again, the swirl tube unit includes a repeating pattern of inertial separation structures which are arranged in a periodic array pattern. In this example, the swirl tube block 108 has the repeating elements arranged in a hexagonal grid pattern. Each repeating element comprises a swirl tube 150 which includes a tubular housing 152 and swirl inducing vanes 154 disposed at the inlet of the tubular housing 152. The vanes 154 can be seen more clearly in the top view shown in Figure 17. As shown in the cross section view in Figure 18, the gas and condensed liquid formed in the heat exchanger 106 are input into the top of the respective swirl tube 150 and the vanes 154 induce a cyclonic or swirling motion of the gas and liquid where the gas and liquid are directed towards the sides of the tubular housing 152. The swirl tube 150 has liquid outlets 156 at various points around the edge of the base of the swirl tube, and a gas outlet 158 which is formed on the axis of the swirl tube. As the liquid droplets have higher mass than the gas, they have higher inertia and so once they are directed towards the edges of the inside of the swirl tube in the swirling motion they are unlikely to make their way to the centre of the tube and reach the gas outlet hole 158. The liquid settles on the inner walls of the swirl tube 150 and runs down the walls to the liquid duct 156 at the edges around the base of the tubes. Meanwhile the gas can pass through the gas outlet hole 158 and then can be outlet through the outlet duct 1 10 of the condenser unit 100. As shown in Figure 18, the spaces between the respective swirl tubes 150 contain voids 160 to reduce the overall mass of the condenser unit 100. Like the weir block, as shown in Figure 16 the swirl tube unit 108 is made with a repeating structure. This example includes four repeating units 170 of swirl tubes, each repeating unit 170 including a number of swirl tubes 150 arranged in a hexagonal packed pattern. Hence, for larger or smaller designs the number of repeating units 170 included in the design could be varied or the number of swirl tubes included in one repeating unit varied, in order to scale to different applications. While Figure 16 shows the four repeating units 170 integrated into a single block of material, separately formed blocks could also be used side by side.

Figure 19 shows a horizontal cross section through the swirl tube units near the base of the unit, in to show the ducting for outputting the liquid. Each swirl tube 150 has liquid removed at six outlets 172 formed at the points of a hexagon surrounding the respective swirl tube and these feed into a hexagonal array of small ducts 174. The small ducts 174 then feed in turn into minor ducts 176 which run along the width of the swirl tube unit 108 between adjacent repeating sections 170. The minor ducts 176 then in turn feed into major ducts 178 which run along the top and bottom of the array at the edge of the swirl tube unit and these link into hose barbs 180 from which the liquid can be tapped and supplied to another part of the system.

Figure 20 shows a method of manufacturing a separator as discussed above. At step 200 a computer automated design (CAD) file is obtained. The CAD file provides a data structure which represents the design of a separator comprising an inertial separation array including a repeating pattern of inertial separation structures is obtained. For example, the design could be created from scratch by a designer generating a three-dimensional (3D) model of the separator, or an existing design could be read from a recording medium or obtained via a network. The design file may represent the 3D geometry of the separator to be manufactured.

At step 202 the CAD file is converted to instructions for supplying to an additive manufacturing machine which control the additive manufacturing machine to deposit or form respective layers of material which are built up layer by layer to form the overall separator. For example, the 3D design represented by the CAD file may be sliced into layers each providing a two-dimensional representation of the material to be formed in the corresponding layer.

At step 204 the converted instructions are supplied to an additive manufacturing machine which manufactures the separator using additive manufacture. The separator can be made from various materials, e.g. metals or alloys, such as titanium or stainless steel, or a polymer for example. Various forms of additive manufacturing can be used, but in one example the additive manufacture uses selective laser melting.

Although illustrative embodiments of the invention have been described in detail herein with reference to the accompanying drawings, it is to be understood that the invention is not limited to those precise embodiments, and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope and spirit of the invention as defined by the appended claims.

Claims

1. A separator for separating liquid droplets from a gas, comprising:

2. The separator according to claim 1 , wherein each inertial separation structure comprises a tubular housing and swirl inducing vanes to induce a swirling flow of gas and liquid droplets within the tubular housing.

3. The separator according to claim 2, wherein each inertial separation structure comprises at least one collecting portion at an inner wall of the tubular housing for collecting the liquid droplets, and at least one gas outlet closer to an axis of the tubular housing than the at least one collecting portion.

4. The separator according to any of claims 2 and 3, wherein the swirl inducing vanes are arranged to direct flow of gas and liquid droplets towards an inner wall of the tubular housing.

5. The separator according to claim 1 , wherein the inertial separator array comprises a plurality of rows;

each row comprising a collection trough running along the row, and at least one gas outlet window arranged between at least one gas inlet for receiving the gas containing the liquid droplets and a base of the collection trough.

6. The separator according to claim 5, wherein said at least one gas outlet window is arranged in a side of the collection trough a distance away from the base of the collection trough.

7. The separator according to any of claims 5 and 6, wherein each inertial separation structure comprises a shielding portion to shield said at least one gas outlet window from an incoming flow of gas containing liquid droplets received from said at least one gas inlet.

8. The separator according to claim 7, wherein the shielding portion comprises a rim portion protruding around at least part of said at least one gas outlet window.

9. The separator according to claim 7, wherein the at least one gas outlet window is disposed on a side of the collector trough facing away from the at least one gas inlet, wherein the shielding portion comprises a side of a collector trough in a neighbouring row facing towards the at least one gas inlet.

10. The separator according to any of claims 1 and 5 to 9, wherein each inertial separation structure comprises at least one gas inlet for receiving the gas containing the liquid droplets, at least one gas outlet for outputting the separated gas, and a collector for collecting the separated liquid droplets;

wherein a fluid flow path from said at least one gas inlet to said at least one gas outlet bends more sharply than a fluid flow path from said at least one gas inlet to said collector.

1 1. The separator according to any of claims 1 to 4, wherein the repeating pattern comprises a grid pattern.

12. The separator according to any preceding claims 1 to 4, wherein the repeating pattern comprises a hexagonal packed pattern.

13. The separator according to any preceding claim, comprising a heat exchanger comprising an array of heat exchanging channels for conveying the gas.

14. The separator according to claim 13, wherein the heat exchanger comprises an array of coolant channels for conveying coolant for cooling the gas in the heat exchanging channels.

15. The separator according to any of claims 13 and 14, wherein each inertial separation structure is configured to perform inertial separation of the liquid droplets from the gas passed through a corresponding group of one or more heat exchanging channels.

16. The separator according to any of claims 13 to 15, wherein each inertial separation structure is configured to perform the inertial separation after the gas is passed through the corresponding group of heat exchanging channels of the heat exchanger.

17. The separator according to any of claims 13 to 15, wherein each inertial separation structure is configured to perform the inertial separation prior to the gas being passed through the corresponding group of one or more heat exchanging channels.

18. The separator according to any of claims 13 to 15, comprising a first inertial separator array arranged to perform the inertial separation prior to the gas being passed through the heat exchanger, and a second inertial separator array arranged to perform the inertial separation after the gas is passed through the heat exchanger.

19. The separator according to any of claims 13 to 18, wherein the inertial separator array is integrally formed with the heat exchanger.

20. The separator according to any of claims 13 to 19, wherein the inertial separator array and the heat exchanger comprise separately formed modules.

21. The separator according to any preceding claim, comprising liquid ducting to direct the liquid separated by each of the plurality of inertial separation structures to a combined liquid outlet.

22. The separator according to any preceding claim, wherein the separator is formed from at least one separator module, each separator module comprising an integrally formed array of two or more inertial separation structures arranged in the repeating pattern.

23. A method of manufacturing a separator for separating liquid droplets from a gas, comprising:

24. The method of claim 23, wherein the inertial separator array is formed by additive manufacturing.

25. A computer-readable data structure representing a design of a separator according to any of claims 1 to 22.

26. A storage medium storing the computer-readable data structure of claim 25.